Patrick Paradis

Distributed fibre optics polarimetric chemical sensor

A new distributed fibre optic chemical sensor based on evanescent wave polarimetric interferometry is proposed with the underlying objective to apply the technology to gas chromatography. It allows real-time monitoring of the displacement of a chemical substance along a capillary. Theoretical analysis, modelling and fabrication of a special fibre containing an off-axis capillary is presented. Proof of the principle is experimentally demonstrated with liquid droplets.

Vapor zone velocities measurement using a capillary optical fiber sensor with an application to gas chromatography

A fiber optic sensor has been used for real-time measurement of the migration rates of all the compounds in a mixture separated by gas chromatography. The sensor makes use of a coated capillary optical fiber as the column. This new type of waveguide consists in a polarization-maintaining optical core positioned close to the capillary edge along the entire fiber length. The optical detection is performed through the coupling of the two polarization modes of the waveguide and this coupling is detected by a polarimetric interferometry technique. Through some signal processing, the resulting interferogram provides the migration rates of the various compounds of a gas mixture flowing in the capillary. One of the major benefits of this optical migration rate sensing is that the detection of each velocity peak appears as soon as the analyte enters the capillary fiber and the peaks are constantly measured during the whole separation process. Carrier gas acceleration occurring in the column is plainly demonstrated. This paper presents a proof-of-concept on a qualitative basis. The experiments were done at 29 degrees C because the current opto-fluidic set-up cannot withstand a higher temperature.

Combined fibre-optic sensor for colour and refractive index (CI) monitoring

Two fibre-optic probes are combined for the simultaneous monitoring of colour and refractive index of liquids, including highly coloured ones. It is shown how, through modelling, the design can be adapted to cover different ranges of refractive index, light absorption and sensitivity.

Ethanol concentration measurement by Raman spectroscopy in liquid-core microstructured optical fiber

A liquid-core air-clad microstructured fiber has been developed for determination of ethanol concentration in aqueous solutions by Raman spectroscopy. The sensor shows a linear response and a low ethanol concentration solution has been characterized using the calibrated sensor. The configuration used for light and liquid injection is stable and robust, making the sensor useful for on-line measurements.

Fiber optic volatile organic compounds sensor based on polymer coated FBG refractometer

Fiber Bragg Grating (FBG) refractometer for liquid refractive index monitoring and its applications have been widely studied in the past few decades. This paper proposes a novel fiber optic volatile organic compounds (VOCs) sensor, achieved by means of polymer film coated high performance FBG refractometer, i.e. cladding removed FBG or even core thinned FBG. Polymer film coated sensor has partial selectivity, which makes this kind of sensors suitable for optical nose systems. While being exposed to VOCs, the sensing layer swells and its refractive index changes at the same time. Transduction part of this sensor, the thinned FBG, works as both strain transducer and refractometer. The mathematical model of the FBG VOCs sensor is introduced and experimentally evaluated with OV-1 coated FBG refractometer, which shows partial selectivity to different vapors and about 100 ppm detection limit to toluene.

Description of the response of a fiber optic velocity sensor applied to capillary gas chromatography.

This paper explores the response of a novel fiber optics sensor allowing real-time determination of the migration rate of vapor zones in capillary gas chromatography. The sensitivity is related to the gradient of the vapor zone distribution in the capillary and it is highest when vapor zones show steep variations in concentration. The expected linearity between the height of the velocity peaks and the response of a thermal conductivity detector is demonstrated experimentally. The sensor can be used to infer an approximate value of the analyte diffusion coefficient from the time response. Finally, the time evolution of the envelope of the optical signal is explained with experimental evidences.

Influence of H2 loading on the performance of a cladding-mode-suppression photosensitive fiber

Cladding mode coupling loss below 0.1 dB for a 30 dB fiber Bragg grating are reported for a wide range of H2 treatment pressure up to 1500 psi. Extension of the photosensitive region into the clading was used for reducing the cladding mode coupling. It is shown that to take proper advantage of this, one must use a wider laser scan beam. Otherwise, the cladding mode coupling loss may increase as the H2 pressure treatment is raised. The benefit of a properly matched photosensitivity obtained by matching the Ge concentration in the core and cladding regions is also highlighted. The fiber was also designed to match a standard single-mode fiber in order to lower the average splicing loss below 0.03 dB and the attenuation to about 0.2 dB/km at 1550 nm.

Optical Fibre Chemical Sensors for Process and Environmental Monitoring

Ion-selective optodes offer potential for in-line monitoring of various processes. Fiber sensors were developed for H+, Ca2+, K+, Na+, NH4+ and NO3−. Applications in hydroponic culture optimization, soil characterization and anaerobic digester process control were demonstrated.

Modeling of polarization mode coupling involved in a capillary optical fibre sensor

Theoretical and experimental work is reported on a distributed polarimetric fibre optic sensor designed for application in capillary gas chromatography. Emphasis is on the improvement of the modeling of the polarization mode coupling mechanism so as to get not only qualitative (vapor identification), but also quantitative (vapor concentration) information from the analysis of a time-modulated signal transmitted through a polarizer at the end of a custom capillary fibre.

Combined fiber optic sensor for Colour and refractive Index (CI) monitoring

Two fiber optic probes are combined for the simultaneous monitoring of colour and refractive index of a liquid. It is shown how, through modelling, the design can be adapted to cover different ranges in refractive index and light absorption.